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Jürgen Geisel, Thomas Bunte, Marion Bodis, Kurt Oette, Wolfgang Herrmann

Apolipoprotein E2/E2 Genotype in Combination with Mutations in the LDL Receptor Gene Causes Type III Hyperlipoproteinemia

The primary genetic cause of type III hyperlipoproteinemia is the homozygous presence of the apolipoprotein E2 allele. However, only approximately 1% of subjects with the apolipoprotein E2/E2 genotype develop type III hyperlipoproteinemia. Other factors are therefore necessary to express type III hyperlipoproteinemia. Two individuals were identified as having type III hyperlipoproteinemia (triglyceride to very low-density lipoprotein (VLDL) cholesterol ratio >0.3). However, in contrast to unchanged or slightly decreased low-density lipoprotein (LDL)-cholesterol levels typically observed in type III patients, elevated LDL-cholesterol levels were observed. The expected apolipoprotein E2/E2 isoform was confirmed by genetic analysis. To explain the elevated LDL-cholesterol level, single strand conformation polymorphism analysis was performed to screen for mutations in the LDL receptor gene. In both individuals, mutations causing an impaired LDL receptor function (2 bp insertion in exon 3 and Glu₁₁₉?Gly mutation in exon 4) were identified. In six more unrelated individuals, these mutations combined with the common apolipoprotein E3/E3 genotype, resulted in an isolated, severe LDLcholesterol elevation. Our results indicate that the level of LDL receptors plays an important role in remnant clearance, and that the combination of the binding-defective apolipoprotein E2 with a defective LDL receptor precipitate type III hyperlipoproteinemia.

Clinical Chemical Laboratory Medicine, Walter de Gruyter

Print ISSN: 1434-6621
Volume: 40, 06/2002
Pages: 475 - 479

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